1. Field of the Invention
Aspects of the present invention relate to a digital broadcast transmitter/receiver and a signal processing method thereof, and more particularly to a digital broadcast transmitter/receiver and a signal processing method thereof which can improve the receiving performance of the system by inserting a known sequence (also referred to as a “supplementary reference sequence (SRS)”) into a VSB (Vestigial Side Band) data stream and transmitting the data stream with the inserted known sequence.
2. Description of the Related Art
An ATSC (Advanced Television Systems Committee) VSB system that is an American-type digital terrestrial broadcasting system is a signal carrier type broadcasting system, and uses a field sync signal in the unit of 312 segments. FIG. 1 is a block diagram illustrating the construction of a transmitter/receiver of an ATSC DTV standard as a general American-type digital terrestrial broadcasting system.
The digital broadcast transmitter of FIG. 1 includes a randomizer 110 for randomizing Moving Picture Experts Group-2 (MPEG-2) transport stream (TS), and a Reed-Solomon (RS) encoder 120 for adding RS parity bytes to the transport stream in order to correct bit errors occurring due to the channel characteristic in a transport process. An interleaver 130 interleaves the RS-encoded data according to a specified pattern. A trellis encoder 140 maps the interleaved data onto 8-level symbols by performing a trellis encoding of the interleaved data at the rate of 2/3. The digital broadcast transmitter performs an error correction coding of the MPEG-2 transport stream.
The digital broadcast transmitter further includes a multiplexer 150 for inserting a segment sync signal and a field sync signal into the error-correction-coded data. A modulator/RF converter 160 inserts a pilot tone into the data symbols into which the segment sync signal and the field sync signal are inserted by inserting specified DC values into the data symbols, performs a VSB modulation of the data symbols by pulse-shaping the data symbols, and up-converts the modulated data symbols into an RF channel band signal to transmit the RF channel band signal. Accordingly, the digital broadcast transmitter randomizes the MPEG-2 transport stream, outer-codes the randomized data through the RS encoder 120 that is an outer coder, and distributes the coded data through the interleaver 130. Also, the digital broadcast transmitter inner-codes the interleaved data in the unit of 12 symbols through the trellis encoder 140, performs the mapping of the inner-coded data onto the 8-level symbols, inserts the field sync signal and the segment sync signal into the coded data, performs the VSB modulation of the data, and then up-converts the modulated data into the RF signal to output the RF signal.
Meanwhile, the digital broadcast receiver of FIG. 1 includes a tuner (not shown) for down-converting an RF signal received through a channel into a baseband signal, and a demodulator 210 for performing a sync detection and demodulation of the converted baseband signal. An equalizer 220 compensates for a channel distortion of the demodulated signal occurring due to a multi-path. A Viterbi decoder 230 corrects errors of the equalized signal and decodes the equalized signal to symbol data. A deinterleaver 250 rearranges the data distributed by the interleaver 130 of the digital broadcast transmitter. An RS decoder 250 corrects errors, and a derandomizer 260 de-randomizes the data corrected through the RS decoder 250 and outputs an MPEG-2 transport stream.
Accordingly, the digital broadcast receiver of FIG. 1 down-converts the RF signal into the baseband signal, demodulates and equalizes the converted signal, and then channel-decodes the demodulated signal to restore to the original signal.
FIG. 2 illustrates a VSB data frame for use in the American type digital broadcasting (8-VSB) system, into which a segment sync signal and a field sync signal are inserted. As shown in FIG. 2, one frame is composed of two fields. One field is composed of one field sync segment that is the first segment and 312 data segments. Also, one data segment in the VSB data frame corresponds to one MPEG-2 packet, and is composed of a segment sync signal of four symbols and 828 data symbols.
In FIG. 2, the segment sync signal and the field sync signal are used for the synchronization and equalization in the digital broadcast receiver. That is, the field sync signal and the segment sync signal refer to known data between the digital broadcast transmitter and receiver, which is used as a reference signal when the equalization is performed in the receiver side.
As shown in FIG. 1, the VSB system of the American type digital terrestrial broadcasting system is a single carrier system. Thus, the system has the drawback in that it is weak in a multi-path fading channel environment having the Doppler effect. Accordingly, the performance of the receiver is greatly influenced by the performance of the equalizer for removing the multi-path fading.
However, according to the existing transport frame as shown in FIG. 2, since the field sync signal that is the reference signal of the equalizer 220 appears once for every 313 segments, its frequency is quite low with respect to one frame signal, and this causes the performance of equalization to deteriorate. Specifically, it is not easy for the existing equalizer 220 to estimate the channel using a small amount of data as above and to equalize the received signal by removing the multi-path fading. Accordingly, the conventional digital broadcast receiver has the disadvantages that its receiving performance deteriorates in an inferior channel environment, and especially in a Doppler fading channel environment.